How to pass an element of an array to an other? - c++

Question

I am trying to take a new plate for a car and change the old one. I need the three letters to be capitals. The thing is that I cannot pass the "capital" element of newPlate array to the new_Plate array. The program compiles but the answer is soometimes %^&#%#$ and some other times nothing. I know I have a problem in the pointers.
void Car::set(char *newBrand, char *newPlate)
{
char new_Brand[80];
char new_Plate[8];
if(strlen(newPlate)==8)
{
for(int i=0;i<3;i++)
{
if(65<=(int)newPlate[i]<=90)
{
new_Plate[i]=newPlate[i]; // probably the problem
}
if(97<=(int)newPlate[i]<=122)
{
new_Plate[i]=(newPlate[i]+32); // probably the problem
}
cout<<new_Plate;
}
}
}

Answer 1

Your new_Plate string does not include a zero terminator.
Furthermore, 65<=(int)newPlate[i]<=90) is not valid in C++. You should write something like
'A'<=newPlate[i] && newPlate[i]<='Z')

Answer 2

The problem with the expression 65<=(int)newPlate[i]<=90 (aside from being unreadable, use more white spaces to make it more readable) is that it means ((65 <= (int) newPlate[i])) <= 90 which is not what it mathematically appears to mean.
This expression will ALWAYS be true because 65 <= (int) newPlate[i] will evaluate to either 1 or 0 and it is of course always < 90.
Also, to make the code even more readable use 'A' instead of 65 and the equivalent for any other character. Most programmers know that 'A' is 65 in ascii but you make them stop one or two seconds to realize that you really mean 'A'!
Also, you must terminate c-strings with a '\0' so you need one extra character at the end or, cout << new_Plate will invoke undefined behavior.
To print c strings the library will output characters from the input buffer until it finds the '\0', since it's not present in your buffer there is no predictable way to print it.
Check this, do you understand the changes?
#include <iostream>
#include <cstring>
using namespace std;
class Car {
public:
Car();
void set(const char *const newBrand, const char *const newPlate);
};
Car::Car()
{
}
void
Car::set(const char *const newBrand, const char *const newPlate)
{
char new_Brand[80];
char new_Plate[9];
size_t length;
size_t i;
(void) new_Brand;
length = strlen(newPlate);
for (i = 0 ; ((i < length) && (i < sizeof(new_Plate) - 1)) ; ++i) {
if (('A' <= newPlate[i]) && (newPlate[i] <= 'Z')) {
new_Plate[i] = newPlate[i];
} else if (('a' <= newPlate[i]) && (newPlate[i] <= 'z')) {
new_Plate[i] = (newPlate[i] - 32);
}
}
new_Plate[i] = '\0';
cout << '*' << new_Plate << '*' << endl;
}
int
main(void)
{
Car car;
car.set("audi", "example text");
return 0;
}